25O COOK 



DIFFERENCES OF ADJUSTMENT TO ENVIRONMENT (ARTISM). 



The notion that all of the differences to be found among the 

 individual members of species are caused by inequalities of en- 

 vironmental experience finds no warrant in the vast mass of 

 experimental facts accumulated by agricultural experience with 

 domesticated plants and animals, nor in observations of species 

 in undisturbed natural conditions. The differences which can 

 be ascribed directly to environmental influences are relatively 

 few and of little importance for evolutionary purposes. Of in- 

 direct effects of environment there are two principal classes, 

 those which arise from the ability of organisms to adjust or 

 accommodate themselves to different environments, and those 

 which result from a disturbance of heredity by new and unac- 

 customed conditions. 



The individual members of species often differ among them- 

 selves as a result of the possession of a certain range of organic 

 elasticity or power of adjustment to different environmental con- 

 ditions. Such differences are commonly greater among plants 

 than among animals, for the latter are often able, through the 

 power of locomotion, to choose or to control the conditions 

 under which they shall exist, while stationary plants are sub- 

 ject to much wider ranges of environmental vicissitudes. It has 

 often been taken for granted that these differences of accommo- 

 dation are direct results of environmental influences, the or- 

 ganism being thought of as having a merely passive plasticity. 

 The fact is, however, that this power of accommodation is as 

 positive a phenomenon, as truly a form of organic activity, as 

 growth, locomotion or reproduction, and as worthy of a definite 

 and appropriate designation in evolutionary literature. 



Indeed it is no mere figure of speech to term these differences 

 accommodations. The word can be used of plants and animals 

 in their environmental relations in quite the same sense as for 

 the change of convexity executed by the human eye to enable 

 objects to be clearly seen at shorter or longer distances. 



This group of intraspecific differences has received a large 

 amount of study from evolutionary specialists, and especially 

 from ecologists and others who hoped to find the causes of evo- 



